Cryogenic refrigerator

ABSTRACT

In a cryogenic refrigerator, a displacer includes a cover portion at a low temperature end of the displacer. A cylinder accommodates the displacer to be reciprocated in a longitudinal direction and forms an expansion space of a refrigerant gas between the cover portion and the cylinder. A refrigerant gas channel through which the displacer and the expansion space communicate with each other is formed in the cover portion. In the refrigerant gas channel, a flowing-out direction of the refrigerant gas flowing into the expansion space is inclined with respect to the longitudinal direction of the displacer.

RELATED APPLICATIONS

Priority is claimed to Japanese Patent Application No. 2013-261441, filed Dec. 18, 2013, the entire content of which is incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a cryogenic refrigerator which generates Simon expansion and g cooling capacity using high pressure refrigerant gas supplied from a compressor, and particularly, to a displacer used in a cryogenic refrigerator.

2. Description of Related Art

As an example of a refrigerator which generates cryogenic temperatures, a Gifford-McMahon (GM) refrigerator is known. In the GM refrigerator, a volume of an expansion space is changed by reciprocating a displacer in a cylinder. The expansion space and a discharge side and a suction side of a compressor are selectively connected to each other according to the volume change, and thus, the refrigerant gas is expanded in the expansion space. A cooling object is cooled by the cold refrigerant gas.

SUMMARY

According to an embodiment of the present invention, there is provided a cryogenic refrigerator including: a displacer; a cover portion which is provided on a low temperature end of the displacer; and a cylinder which accommodates the displacer to be reciprocated in the longitudinal direction and to form an expansion space of a refrigerant gas between the cover portion and the cylinder. A refrigerant gas channel, through which the displacer and the expansion space communicate with each other, is formed in the cover portion, and a flowing-out direction of the refrigerant gas flowing into the expansion space is inclined with respect to the longitudinal direction of the displacer in the refrigerant gas channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a cryogenic refrigerator and a displacer according to an embodiment of the present invention.

FIGS. 2A and 2B are diagrams illustrating an example of a refrigerator gas channel in the cryogenic refrigerator according to the embodiment of the present invention.

FIGS. 3A and 3B are diagrams illustrating another example of the refrigerator gas channel according to the embodiment of the present invention.

FIG. 4 is a schematic diagram illustrating a configuration of a two-stage cryogenic refrigerator according to another embodiment of the present invention.

FIGS. 5A and 5B are schematic diagrams illustrating another configuration of the two-stage cryogenic refrigerator according to the embodiment of the present invention.

FIG. 6 is a schematic diagram illustrating a cryogenic refrigerator and a displacer according to a modification of the embodiment of the present invention.

DETAILED DESCRIPTION

In a refrigerator including a displacer such as a Gifford-McMahon refrigerator, in order to reciprocate the displacer in a cylinder, a clearance is provided between the cylinder and the displacer. A cooling stage is provided on a low temperature end of the cylinder, and a portion of the clearance functions as a heat exchanger which performs heat exchange between a refrigerant gas in the clearance and the cooling stage. Meanwhile, it is also known that a loss referred to as a shuttle loss may occur due to heat conduction of the refrigerant gas existing in the clearance.

If the heat exchanger is lengthened and a heat exchange area between the refrigerant gas and the cooling stage is widened, the heat exchange efficiency between the refrigerant gas and the cooling stage will be improved. However, the shuttle loss is increased as the heat exchanger is lengthened. In this way, there is a trade-off relationship between an improvement of the heat exchange efficiency and a decrease of the shuttle loss by the change of the length of the heat exchanger.

It is desirable to provide a technology which improves the heat exchange efficiency between a refrigerant gas and a heat exchanger while decreasing a shuttle loss.

According to an embodiment of the present invention, it is possible to provide a technology which improves the heat exchange efficiency between a refrigerant gas and a heat exchanger while decreasing shuttle loss.

An embodiment of the present invention will be described with reference to the drawings.

For example, a cryogenic refrigerator 1 according to the embodiment is a Gifford-McMahon (GM) type refrigerator using helium gas as a refrigerant gas. The cryogenic refrigerator 1 includes a displacer 2, a cylinder 4 which forms an expansion space 3 between the displacer 2 and the cylinder 4, and a bottomed cylindrical cooling stage 5 which is adjacent to the expansion space 3 and is positioned to externally enclose the space. The cooling stage 5 functions as a heat exchanger which performs heat exchange between a cooling object and the refrigerant gas. The displacer 2 includes a main body portion 2 a and a cover portion 2 b which is provided on a low temperature end. The cover portion 2 b may be configured of the same member as the main body portion 2 a. Moreover, the cover portion 2 b may be configured of a material having higher thermal conductivity than the main body portion 2 a. Accordingly, the cover portion 2 b also functions as a heat conduction portion which performs heat exchange between the refrigerant gas flowing to the inside of the cover portion 2 b and the cover portion. For example, the cover portion 2 b is configured of a material having at least higher thermal conductivity than the main body portion 2 a, such as copper, aluminum, or stainless steel. For example, the cooling stage 5 is configured of copper, aluminum, stainless steel, or the like.

A compressor 12 recovers a low pressure refrigerant gas from a suction side, and after the compressor compresses the refrigerant gas, the compressor supplies a high pressure refrigerant gas to the cryogenic refrigerator 1. For example, a helium gas may be used as the refrigerant gas. However, the refrigerant gas is not limited thereto.

The cylinder 4 accommodates the displacer 2 to be reciprocated in a longitudinal direction. From the viewpoint of strength, thermal conductivity, helium shielding capability, or the like, for example, the cylinder 4 is configured of stainless steel.

A scotch yoke mechanism (not illustrated) which reciprocates the displacer 2 is provided on a high temperature end of the displacer 2, and the displacer 2 reciprocates along an axial direction of the cylinder 4.

The displacer 2 has a cylindrical outer circumferential surface and a regenerator material is filled in the displacer 2. An internal volume of the displacer 2 configures a regenerator 7. Straightening devices (not illustrated) which straighten the flow of the helium gas may be provided on the upper end side and the lower end side of the regenerator 7.

An upper opening 11, which circulates the refrigerant gas from a room temperature chamber 8 to the displacer 2, is formed on the high temperature end of the displacer 2. The room temperature chamber 8 is a space which is formed of the cylinder 4 and the high temperature end of the displacer 2, and a volume of the room temperature chamber is changed according to the reciprocation of the displacer 2.

In pipes which connect suction and discharge systems configured of the compressor 12, a supply valve 13, and a return valve 14 to each other, a supply-exhaust common pipe is connected to the room temperature chamber 8. In addition, a seal 15 is mounted between a portion on the high temperature end of the displacer 2 and the cylinder 4.

A refrigerant gas channel 16 which introduces the refrigerant gas into the expansion space 3 is formed on the low temperature end of the displacer 2. The expansion space 3 is a space which is formed of the cylinder 4 and the displacer 2, and a volume of the expansion space is changed according to the reciprocation of the displacer 2. The cooling stage 5 which is thermally connected to the cooling object is disposed at a position corresponding to the expansion space 3 of the outer circumference and the bottom portion of the cylinder 4, and the cooling stage 5 is cooled by the refrigerant gas flowing into the expansion space 3 through the refrigerant gas channel 16.

From the viewpoint of specific gravity, strength, thermal conductivity, or the like, for example, the main body portion 2 a of the displacer 2 may be formed of a phenol resin or the like. For example, the regenerator material is configured of a wire screen or the like. In addition, FIG. 1 illustrates the state during the operation of the cryogenic refrigerator 1. Accordingly, both outer diameters are the same as each other according to slight shrinkage of the main body portion 2 a from the low temperature. However, in normal temperatures, the outer diameter of the cover portion 2 b is slightly smaller than the outer diameter of the main body portion 2 a.

Next, the operation of the cryogenic refrigerator 1 will be described. In a certain point of time of a refrigerant gas supply process, the displacer 2 is positioned at a bottom dead center LP of the cylinder 4. If the supply valve 13 is opened at the same time as that, or at timing slightly deviated from that, the high pressure refrigerant gas is supplied from the supply-exhaust common pipe into the cylinder 4 via the supply valve 13. As a result, the high pressure refrigerant gas flows from the upper opening 11 positioned at the upper portion of the displacer 2 into the regenerator 7 positioned in the displacer 2. The high pressure refrigerant gas flowing into the regenerator 7 is supplied to the expansion space 3 via the refrigerant gas channel 16 positioned at the lower portion of the displacer 2 while being cooled by the regenerator material.

If the expansion space 3 is filled with the high pressure refrigerant gas, the supply valve 13 is closed. In this case, the displacer 2 is positioned at a top dead center UP in the cylinder 4. If the return valve 14 is opened at the same time as that, or at timing slightly deviated from that, the refrigerant gas in the expansion space 3 is decompressed and expanded. The helium gas in the expansion space 3, which drops to a low temperature by the expansion, absorbs heat from the cooling stage 5.

The displacer 2 moves toward the bottom dead center LP, and thus, the volume of the expansion space 3 is decreased. The refrigerant gas in the expansion space 3 is returned to the suction side of the compressor 12 via the refrigerant gas channel 16, the regenerator 7, and the upper opening 11. In this case, the regenerator material is cooled by the refrigerant gas. This process is set to one cycle, and the cryogenic refrigerator 1 cools the cooling stage 5 by repeating the cooling cycle.

In the cryogenic refrigerator 1 and the displacer 2 according to the embodiment, the heat entering from the cooling stage 5 enters the cover portion 2 b via the refrigerant gas existing in the expansion space 3. That is, when the low temperature refrigerant gas generated in the expansion space 3 passes through the refrigerant gas channel 16, heat exchange between the refrigerant gas and the cover portion 2 b is performed.

In addition, the heat entering the cover portion 2 b is further transmitted toward the expansion space 3 through the inner portion of the cover portion 2 b. As described above, the cover portion 2 b is provided on the low temperature end of the displacer 2. Accordingly, the cover portion 2 b comes into contact with the low temperature refrigerant gas in the expansion space 3, and it is possible to further improve the heat exchange efficiency between the cooling stage 5 and the refrigerant gas.

In addition, for example, the cover portion 2 b of the displacer 2 may be configured of a phenol resin or the like. However, compared to the cryogenic refrigerator 1 according to the present embodiment in which the cover portion 2 b is configured of a material having higher thermal conductivity than the main body portion 2 a, the heat exchange between the refrigerant gas and the cover is decreased, and the heat exchange is not substantially performed. Accordingly, only the heat exchange between the low temperature refrigerant gas generated in the expansion space 3 and the cooling stage 5 is performed, and thus, the cooling efficiency is decreased. Therefore, preferably, in the cover of the displacer 2, the cover portion 2 b is configured of a material having higher thermal conductivity than the main body portion 2 a.

As described above, in the cryogenic refrigerator 1 according to the present embodiment, the refrigerant gas in the expansion space 3 is expanded by reciprocating the displacer 2 in the cylinder 4, and thus, cooling capacity is generated. As illustrated in FIG. 1, a clearance C is provided between the cylinder 4 and the displacer 2 to reciprocate the displacer 2. A portion of the clearance C adjacent to the cooling stage 5 functions as a heat exchanger which performs heat exchange between the cooling stage 5 and the refrigerant gas in the clearance C.

Here, in order to cause the refrigerant gas in the displacer 2 to pass through the heat exchanger, a technology in which the refrigerant gas channel 16 is directed in a radial direction of the cylinder 4 (a direction directed to the side surface of the cylinder 4) is also known. According to this method, there is an advantage that the heat exchange area is increased. However, the refrigerant gas channel 16 is bent, and the channel area is likely to be narrowed. As a result, a channel resistance is increased, and pressure loss occurs. In addition, when the displacer 2 reciprocates the cylinder 4, loss due to heat conduction of the refrigerant gas existing in the clearance C occurs, that is, so-called “shuttle loss” occurs.

On the other hand, in order to decrease the shuttle loss, a technology in which the refrigerant gas channel 16 is provided in the axial direction of the cylinder 4 and the refrigerant gas flows out to the bottom surface of the cylinder 4 is also known. In this method, since the heat exchange is not positively performed by the clearance C, the channel resistance of the refrigerant gas channel 16 can be decreased. Accordingly, compared to the method in which the refrigerant gas channel 16 is directed in the radial direction of the cylinder 4, the pressure loss or the shuttle loss is decreased. However, the heat exchange area between the refrigerant gas expanded in the expansion space 3 and the cooling object is narrowed, and the heat exchange efficiency is decreased.

Accordingly, in the refrigerant gas channel 16, through which the displacer 2 and the expansion space 3 communicate with each other, according to the embodiment, when the refrigerant gas flowing from the displacer 2 into the expansion space 3, the direction of the refrigerant gas channel 16 is provided to be inclined with respect to the longitudinal direction of the displacer 2. Hereinafter, the refrigerant gas channel 16 according to the embodiment will be described more specifically.

FIG. 1 illustrates an example of the refrigerant gas channel 16 according to the embodiment. As illustrated in FIG. 1, in the cover portion 2 b of the displacer 2, a first opening 17 is provided on the inside surface (hereinafter, referred to as an “inner surface 19”) of the displacer 2, and a second opening 18 is provided on the outside surface (hereinafter, referred to as an “outer surface 20”) of the displacer 2. The refrigerant gas channel 16 has the first opening 17 at one end and the second opening 18 at the other end, and is provided so that the inner surface 19 and the outer surface 20 communicate with each other in the cover portion 2 b.

Here, when the first opening 17 on the inner surface 19 is projected to the outer surface 20 along the longitudinal direction of the displacer 2, the refrigerant gas channel 16 is provided so that the position of the first opening 17 and the position of the second opening 18 after the projection are different from each other. Accordingly, when the refrigerant gas flows from the first opening 17 and the second opening 18 into the expansion space 3, the refrigerant gas flows out in a direction different from the longitudinal direction of the displacer 2. As a result, in the cryogenic refrigerator 1 according to the embodiment, compared to the case where the refrigerant gas channel 16 is provided downward in FIG. 1 along the axial direction of the cylinder 4, a vortex of the refrigerant gas in the expansion space 3 is easily generated due to the operation of the refrigerant gas which flows out of the second opening 18 into the expansion space 3. Accordingly, the heat exchange efficiency between the refrigerant gas and the cooling stage 5 is improved.

Moreover, compared to the case where the refrigerant gas channel 16 is directed in the radial direction of the cylinder 4, in the cryogenic refrigerator 1 according to the embodiment, the channel area of the refrigerant gas channel 16 can be increased, and thus, the shuttle loss and the pressure loss can be decreased.

Here, preferably, the refrigerant gas channel 16 is provided so that the refrigerant gas flowing out from the second opening 18 is directed to the side surface of the cylinder 4. Accordingly, the refrigerant gas flowing out from the second opening 18 comes into contact with the side surface of the cylinder 4 and the movement direction of the refrigerant gas is changed, and thus, the motion of the refrigerant gas in the expansion space 3 becomes complicated. Therefore, the vortex of the refrigerant gas in the expansion space 3 is more easily generated, and the heat exchange efficiency between the refrigerant gas and the cooling stage 5 is further improved.

Moreover, preferably, a plurality of the refrigerant gas channels 16, through which the first opening 17 and the second opening 18 communicate with each other, are provided on the cover portion 2 b of the displacer 2. Accordingly, the entire channel area of the refrigerant gas channels 16 can be increased, and it is possible to further decrease the pressure loss. Moreover, the refrigerant gas flows out of the plurality of locations into the expansion space 3, and thus, the motion of the refrigerant gas in the expansion space 3 becomes complicated. Accordingly, turbulent flow of the refrigerant gas in the expansion space 3 is easily generated, and the heat exchange efficiency between the refrigerant gas and the cooling stage 5 is further improved.

FIGS. 2A and 2B are diagrams illustrating other examples of the refrigerant gas channel 16 in the cryogenic refrigerator 1 according to the embodiment of the present invention. Also in the examples illustrated in FIGS. 2A and 2B, similar to the example illustrated in FIG. 1, the refrigerant gas channel 16 has the first opening 17 as one end and the second opening 18 as the other end, and is provided so that the inner surface 19 and the outer surface 20 communicate with each other in the cover portion 2 b. In addition, when the first opening 17 on the inner surface 19 is projected to the outer surface 20 along the longitudinal direction of the displacer 2, the position of the first opening 17 and the position of the second opening 18 after the projection are different from each other.

However, the examples illustrated in FIGS. 2A and 2B are different from the example illustrated in FIG. 1. That is, the direction in which the refrigerant gas passing through one refrigerant gas channel 16 flows into the expansion space 3 is the same as the direction in which the refrigerant gas passing through other refrigerant gas channels 16 flow into the expansion space 3. Accordingly, due to the motion of the refrigerant gas which flows into the expansion space 3, a force operates in the direction in which the refrigerant gas in the expansion space 3 is rotated, and thus, the vortex is easily generated in the refrigerant gas in the expansion space 3. In addition, the refrigerant gas channel 16 is formed in a spiral shape in the example illustrated in FIG. 2B while the refrigerant gas channel 16 is linearly formed in the example illustrated in FIG. 2A. Compared to the example illustrated in FIG. 2B, the example illustrated in FIG. 2A has an advantage in that machining of the refrigerant gas channel 16 is easily performed. On the other hand, compared to the example illustrated in FIG. 2A, in the example illustrated in FIG. 2B, the refrigerant gas channel 16 is lengthened. Accordingly, the example illustrated in FIG. 2B has an advantage in that the heat exchange efficiency between the refrigerant gas flowing through the refrigerant gas channel 16 and the cover portion 2 b is improved.

FIGS. 3A and 3B are diagrams illustrating other examples of the refrigerant gas channel 16 according to the embodiment of the present invention, and are perspective diagrams illustrating the refrigerant gas channel 16 and the cover portion 2 b. More specifically, FIGS. 3A and 3B are diagrams which illustrate a case where four refrigerant gas channels 16 (channels 16 a, 16 b, 16 c, and 16 d of the refrigerant gas) are provided in the cover portion 2 b. Moreover, compared to the examples illustrated in FIGS. 1 to 2B, in FIGS. 3A and 3B, the shape of the cover portion 2 b are illustrated so as to be partially omitted.

Here, FIG. 3A illustrates an example in which four refrigerant gas channels 16 are linearly formed from the first opening 17 to the second opening 18. Moreover, FIG. 3B illustrates an example in which four refrigerant gas channels 16 are formed in a spiral shape from the first opening 17 to the second opening 18. In FIGS. 3A and 3B, among four refrigerant gas channels 16, the direction in which the refrigerant gas passing through one refrigerant gas channel 16 flows into the expansion space 3 is different from a direction in which the refrigerant gas passing through another refrigerant gas channel 16 flows into the expansion space 3.

For example, in FIG. 3A, the refrigerant gas passing through the refrigerant gas channel 16 a flows out in a lower right direction in FIG. 3A in the expansion space 3. On the other hand, the refrigerant gas passing through the refrigerant gas channel 16 c flows out to a side opposite to the flowing-out direction of the refrigerant gas passing the refrigerant gas channel 16 a in the expansion space 3, that is, in a lower left direction in FIG. 3A. Accordingly, due to the motion of the refrigerant gas which flows into the expansion space 3, a force operates in the direction in which the refrigerant gas in the expansion space 3 is rotated, and thus, the vortex is easily generated in the refrigerant gas in the expansion space 3.

More specifically, in FIG. 3A, four refrigerant gas channels 16 are provided to be rotationally symmetrical with respect to a central axis in the longitudinal direction of the displacer 2. Here, the central axis in the longitudinal direction of the displacer 2 coincides with a central axis when the cover portion 2 b is assumed as a column. Accordingly, four refrigerant gas channels 16 in FIG. 3A are provided to be rotationally symmetrical with respect to the central axis of the cover portion 2 b.

For example, if the cover portion 2 b illustrated in FIG. 3A is rotated by 90° in a clockwise direction about the central axis, the positions of the refrigerant gas channels 16 a, 16 b, 16 c, and 16 d after the rotation coincide with the positions of the refrigerant gas channels 16 b, 16 c, 16 d, and 16 a before the rotation. Also in a case where the cover portion is rotated by 180° or 270°, the positions similarly coincide, and each of the positions of the refrigerant gas channels 16 a, 16 b, 16 c, and 16 d after the rotation coincide with any one of the positions of the refrigerant gas channels 16 a, 16 b, 16 c, and 16 d before the rotation.

Accordingly, the refrigerant gas, which passes through the refrigerant gas channels 16 a, 16 b, 16 c, and 16 d and flows into the expansion space 3, is operated to rotate the refrigerant gas in the expansion space 3 in the same rotation direction. As a result, the vortex is easily generated in the refrigerant gas in the expansion space 3, and it is possible to further improve the heat exchange efficiency between the refrigerant gas and the cover portion 2 b in the expansion space 3.

Moreover, similar to the example illustrated in FIG. 3A, also in the example illustrated in FIG. 3B, four refrigerant gas channels 16 are provided to be rotationally symmetric with respect to the central axis in the longitudinal direction of the displacer 2. Accordingly, the effects also are similar to those of the example illustrated in FIG. 3A. That is, the vortex is easily generated in the refrigerant gas in the expansion space 3, and it is possible to further improve the heat exchange efficiency between the refrigerant gas and the cover portion 2 b in the expansion space 3.

As the above, it is described on the assumption that the cryogenic refrigerator 1 according to the embodiment is a one-stage refrigerator. The cryogenic refrigerator 1 is not limited to the one-stage refrigerator but may be a multi-stage refrigerator. For example, as described below, the cryogenic refrigerator 1 may be applied to a two-stage refrigerator.

FIG. 4 is a schematic diagram illustrating a two-stage cryogenic refrigerator 31 according to another embodiment of the present invention. Similar to the above-described one-stage cryogenic refrigerator 1, the cryogenic refrigerator 31 is a Gifford-McMahon (GM) type refrigerator using helium gas as a refrigerant gas. As illustrated in FIG. 4, the cryogenic refrigerator 31 includes a first displacer 32, and a second displacer 36 which is connected to the first displacer 32 in the longitudinal direction. For example, as illustrated in FIGS. 5A and 5B, the first displacer 32 and the second displacer 36 are connected to each other via a pin 33, a connector 34, and a pin 35.

A first cylinder 37 is integrally formed with a second cylinder 38, and the low temperature end of the first cylinder 37 and the high temperature end of the second cylinder 38 are connected to each other at the bottom portion of the first cylinder 37. The second cylinder 38 is coaxially formed with the first cylinder 37 and is a cylinder member having a smaller diameter than the first cylinder 37. The first cylinder 37 accommodates the first displacer 32 to be reciprocated in the longitudinal direction, and the second cylinder 38 accommodates the second displacer 36 to be reciprocated in the longitudinal direction.

Considering strength, thermal conductivity, helium shielding capability, or the like, for example, the first cylinder 37 and the second cylinder 38 are formed of stainless steel. The second displacer 36 is configured so that a film of an abrasion-resistant resin such as a fluorocarbon resin is covered on the outer circumferential surface of a pipe formed of metal such as stainless steel.

The first displacer 32 has a cylindrical outer circumferential surface, and a first regenerator material (not illustrated) is filled in the first displacer 32. The internal volume of the first displacer 32 functions as a first regenerator 41. Although it is not illustrated, straightening devices may be installed on the upper portion and the lower portion of the first regenerator 41. An upper opening 42, which circulates the refrigerant gas from a room temperature chamber 39 to the first displacer 32, is formed on the high temperature end of the first displacer 32. The room temperature chamber 39 is a space which is formed of the first cylinder 37 and the high temperature end of the first displacer 32, and the volume of the room temperature chamber is changed according to the reciprocation of the first displacer 32. In pipes which connect suction and exhaust systems configured of a compressor 43, a supply valve 44, and a return valve 45 to each other, a supply-exhaust common pipe is connected to the room temperature chamber 39. In addition, a seal 46 is mounted between a portion on the high temperature end of the first displacer 32 and the first cylinder 37.

A refrigerant gas channel 48 which introduces the refrigerant gas into a first expansion space 47 is formed on the low temperature end of the first displacer 32. The first expansion space 47 is a space which is formed of the first cylinder 37 and the first displacer 32, and the volume of the expansion space is changed according to the reciprocation of the first displacer 32. A first cooling stage 49 which is thermally connected to an object to be cooled (not illustrated) is disposed at a position corresponding to the first expansion space 47 of the outer circumference of the first cylinder 37, and the first cooling stage 49 is cooled by the refrigerant gas of the first expansion space 47.

The second displacer 36 has a cylindrical outer circumferential surface, and a second regenerator material (not illustrated) is filled in the second displacer 36. The internal volume of the second displacer 36 configures a second regenerator 50. The first expansion space 47 and the high temperature end of the second displacer 36 communicate with each other through a communication path (not illustrated). The refrigerant gas circulates from the first expansion space 47 to the second regenerator 50 via the communication path.

A refrigerant gas channel 56 for circulating the refrigerant gas into a second expansion space 51 is formed on the low temperature end of the second displacer 36. The second expansion space 51 is a space which is formed of the second cylinder 38 and the second displacer 36, and the volume of the expansion space is changed according to the reciprocation of the second displacer 36.

A second cooling stage 54 which is thermally connected to the cooling object is disposed at a position corresponding to the second expansion space 51 of the outer circumference of the second cylinder 38, and the second cooling stage 54 is cooled by the refrigerant gas in the second expansion space 51.

From the viewpoint of specific gravity, strength, thermal conductivity, or the like, the first displacer 32 is formed of fabric based on phenol or the like. For example, the first regenerator material is configured of a wire screen or the like. In addition, for example, the second regenerator material is configured by interposing a regenerator material such as a lead ball in the axial direction by a felt and a wire screen. Moreover, a spiral groove 53 extending to the first expansion space 47 side in a spiral shape is formed on the outer circumference surface of the second displacer 36.

In the example illustrated in FIG. 4, the refrigerant gas channel 48 is configured to communicate with the cover portion 32 b positioned at the low temperature end of the first displacer 32. The refrigerant gas channel 56 is configured to communicate with the cover portion 52 b positioned at the low temperature end of the second displacer 36. Similar to the refrigerant gas channel 16 illustrated in FIG. 1, the refrigerant gas channel 48 and the refrigerant gas channel 56 are provided to be inclined with respect to the longitudinal directions of the first displacer 32 and the second displacer 36. Accordingly, the refrigerant gas passing the refrigerant gas channel 48 generates a vortex of the refrigerant gas in the first expansion space 47. Similarly, the refrigerant gas passing the refrigerant gas channel 56 generates a vortex of the refrigerant gas in the second expansion space 51.

As a result, it possible to improve the heat exchange efficiency between the refrigerant gas in the first expansion space 47 and the first cooling stage 49, and the heat exchange efficiency between the refrigerant gas in the second expansion space 51 and the second cooling stage 54. Moreover, it is possible to decrease shuttle loss between the first cylinder 37 and the first displacer 32 and shuttle loss between the second cylinder 38 and the second displacer 36.

FIGS. 5A and 5B are schematic diagrams illustrating other configurations of the two-stage cryogenic refrigerator 31 according to the embodiment of the present invention. Compared to the example illustrated in FIG. 4, in the examples illustrated in FIGS. 5A and 5B, the shapes of the refrigerant gas channels 56 communicating with the cover portions 52 b positioned at the low temperature ends of the second displacers 36 are different, and other portions are in common. Accordingly, the common portions are appropriately omitted or simplified and are described.

The shape of the refrigerant gas channel 56 in the example illustrated in FIG. 5A is similar to the shape of the refrigerant gas channel 16 illustrated in FIG. 2A. Moreover, the shape of the refrigerant gas channel 56 in FIG. 5B is similar to the shape of the refrigerant gas channel 16 illustrated in FIG. 2B. Accordingly, the effects are similar with each other, and it is possible to improve the heat exchange efficiency between the refrigerant gas in the second expansion space 51 and the second cooling stage 54. Moreover, it is possible to decrease shuttle loss between the first cylinder 37 and the first displacer 32 and shuttle loss between the second cylinder 38 and the second displacer 36.

As described above, in the cryogenic refrigerator 1 and the cryogenic refrigerator 31 according to the embodiments, it is possible to improve the heat exchange efficiency between the refrigerant gas and the heat exchanger while decreasing the shuttle loss.

In the above, the present invention is described based on the embodiments. However, the embodiments only illustrate a principle or application of the present invention. Moreover, in the embodiments, various modifications or changes in the disposition can be performed within a scope which does not depart from the gist of the present invention defined in claims.

For example, the above-described cryogenic refrigerators illustrate the cases where the number of the stages is one or two. However, the number of the stages can be appropriately changed to three or the like. Moreover, the embodiments describe examples in which the cryogenic refrigerator is the GM refrigerator. However, the embodiments of the present invention are not limited thereto. For example, the embodiments of the present invention can be applied to any refrigerator having the displacer such as a Stirling refrigerator or a Solvay refrigerator.

In the above, FIGS. 4 to 5B describe the case of the refrigerant gas channel 48 in which the shape of the refrigerant gas channel 48 communicating with the cover portion 32 b positioned at the low temperature end of the first displacer 32 is similar to the shape of the refrigerant gas channel 16 illustrated in FIG. 1. However, the shape of the refrigerant gas channel 48 in the two-stage cryogenic refrigerator 31 is not limited thereto. That is, for example, the shape of the refrigerant gas channel 48 may be the shapes illustrated in FIGS. 2A and 2B or FIGS. 3A and 3B, and the effects also are similar to those of cases illustrated in FIGS. 2A and 2B or FIGS. 3A and 3B.

In the above, the case is described in which the first opening 17 which is one end of the refrigerant gas channel 16 is provided on the inner surface 19 in the cover of the low temperature end side of the displacer 2 and the second opening 18 which is the other end is provided on the outer surface 20. Here, the refrigerant gas channel 16 may be provided so that the direction of the refrigerant gas flowing out of the second opening 18 is inclined with respect to the longitudinal direction of the displacer 2, and is not limited as long as the first opening 17 or the second opening 18 is directed onto the cover of the low temperature end side of the displacer 2.

FIG. 6 is a schematic diagram illustrating the cryogenic refrigerator 1 and the displacer 2 according to a modification of the embodiment of the present invention. As illustrated in FIG. 6, in the cryogenic refrigerator 1 according to the modification, the first opening 17 and the second opening 18 positioned at both ends of the refrigerant gas channel 16 are provided on the main body portion 2 a of the displacer 2. Here, the first opening 17 and the second opening 18 are different from each other along the longitudinal direction of the displacer 2, and the refrigerant gas channel 16 is directed in an inclined downward direction in FIG. 6.

The second opening 18 is positioned in the clearance C, and the gas, which flows from the first opening 17 and passes through the refrigerant gas channel 16, flows out of the second opening 18 toward the side surface of the cylinder 4. Accordingly, the refrigerant gas flowing out of the second opening 18 comes into contact with the side surface of the cylinder 4, the movement direction of the refrigerant gas is changed, and thus, the motion of the refrigerant gas in the expansion space 3 becomes complicated. Therefore, a vortex of the refrigerant gas in the expansion space 3 is more easily generated, and it is possible to improve the heat exchange efficiency between the refrigerant gas and the cooling stage 5. Moreover, it is possible to decrease the shuttle loss.

In the above, as illustrated in FIG. 1, the case is described in which the first opening 17 which is one end of the refrigerant gas channel 16 is provided on the inner surface 19 in the cover of the low temperature end side of the displacer 2, and the second opening 18 which is the other end is provided on the outer surface 20. In addition, for example, as illustrated in FIG. 6, the refrigerant gas channel in which both ends of the refrigerant gas channel are provided on the main body portion 2 a of the displacer 2 may be further provided. In this case, the refrigerant gas channel provided on the main body portion 2 a may be a so-called “horizontal jet channel” which is orthogonal with respect to the axial direction of the displacer 2.

Moreover, in the cryogenic refrigerator 1 according to the modification, the number of the stages is one. However, the modification can be also applied to a case where the number of the stages is two or more. In each stage, the refrigerant gas channel 16 is provided on the side surface of the cylinder, and the refrigerant gas channel may be provided so that the direction of the refrigerant gas flowing out of the second opening 18 is inclined with respect to the longitudinal direction of the displacer 2. In addition, the first opening 17 is provided on the inner surface 19 of the cover, and the second opening 18 may be provided on the side surface of the cylinder.

It should be understood that the invention is not limited to the above-described embodiment, but may be modified into various forms on the basis of the spirit of the invention. Additionally, the modifications are included in the scope of the invention. 

What is claimed is:
 1. A cryogenic refrigerator comprising: a displacer; a cover portion which is provided on a low temperature end of the displacer; and a cylinder which accommodates the displacer to be reciprocated in a longitudinal direction and to form an expansion space of a refrigerant gas between the cover portion and the cylinder, wherein a refrigerant gas channel, through which the displacer and the expansion space communicate with each other, is formed in the cover portion, and wherein a flowing-out direction of the refrigerant gas flowing into the expansion space is inclined with respect to the longitudinal direction of the displacer in the refrigerant gas channel.
 2. The cryogenic refrigerator according to claim 1, wherein the refrigerant gas channel is provided so that the refrigerant gas flowing into the expansion space is directed to a side surface of the cylinder.
 3. The cryogenic refrigerator according to claim 1, wherein the cover portion includes a plurality of the refrigerant gas channels.
 4. The cryogenic refrigerator according to claim 3, wherein among the plurality of refrigerant gas channels, a direction in which the refrigerant gas passing through one channel flows into the expansion space is different from a direction in which the refrigerant gas passing through other channels flows into the expansion space.
 5. The cryogenic refrigerator according to claim 3, wherein the plurality of refrigerant gas channels are provided to be rotationally symmetrical with respect to a central axis in the longitudinal direction of the displacer. 